Method for thin film protective overcoat

ABSTRACT

A system and method for improving the durability and reliability of recording media used in hard drives is disclosed. A protective overcoat made by depositing a diamond like carbon (DLC) layer over a magnetic layer and then depleting the DLC protective layer of hydrogen before it is coated with a Perfluoropolyethers (PFPE) using an in-situ vapor lubrication technique.

This application claims priority from U.S. provisional applicationserial number 60/337,323, filed on Dec. 5, 2001.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to magnetic discs for use in computer discdrives, and, more particularly, to application of the lubricant layerover the magnetic disc

2. Description of the Related Art

Computer disc drives commonly use components made out of thin films tostore information. Both the read-write element and the magnetic storagemedia of disc drives are typically made from thin films.

FIG. 1A is an illustration showing the layers of a conventional magneticmedia structure including a substrate 105, a seed layer 109, a magneticlayer 113, a diamond like carbon (DLC) protective layer 117, and a lubelayer 121. The initial layer of the media structure is the substrate105, which is typically made of nickel-phosphorous plated aluminum orglass that has been textured. The seed layer 109, typically made ofchromium, is a thin film that is deposited onto the substrate 105creating an interface of intermixed substrate 105 layer molecules andseed layer 109 molecules between the two. The magnetic layer 113,typically made of a magnetic alloy containing cobalt (Co), platinum (Pt)and chromium (Cr), is a thin film deposited on top of the seed layer 109creating a second interface of intermixed seed layer 109 molecules andmagnetic layer 113 molecules between the two. The DLC protective layer117, typically made of carbon and hydrogen, is a thin film that isdeposited on top of the magnetic layer 113 creating a third interface ofintermixed magnetic layer 113 molecules and DLC protective layer 117molecules between the two. Finally the lube layer 121, typically made ofa polymer containing carbon (C) and fluorine (F) and oxygen (O), isdeposited on top of the DLC protective layer 117 creating a fourthinterface of intermixed DLC protective layer 117 molecules and lubelayer 121 molecules.

The durability and reliability of recording media is achieved primarilyby the application of the DLC protective layer 117 and the lube layer121. The combination of the DLC protective layer 117 and lube layer 121is referred to as a protective overcoat. The DLC protective layer 117 istypically an amorphous film called diamond like carbon (DLC), whichcontains carbon and hydrogen and exhibits properties between those ofgraphite and diamond. Thin layers of DLC are deposited on disks usingconventional thin film deposition techniques such as ion beam deposition(IBD), plasma enhanced chemical vapor deposition (PECVD), magnetronsputtering, radio frequency sputtering or chemical vapor deposition(CVD). During the deposition process, adjusting sputtering gas mixturesof argon and hydrogen varies the concentrations of hydrogen found in theDLC. Since typical thicknesses of DLC protective layer 117, are lessthan 100 Angstroms, lube layer 121 is deposited on top of the DLCprotective layer 117, for added protection, lubrication and enhanceddisk drive reliability. Lube layer 121 further reduces wear of the discdue to contact with the magnetic head assembly.

A typical lubricant used in lube layer 121 is Perfluoropolyethers(PFPEs), which are long chain polymers composed of repeat units of smallperfluorinated aliphatic oxides such as perfluoroethylene oxide orperfluoropropylene oxide. The entire disclosure of U.S. Pat. No.5,776,577 titled “Magnetic Recording Disk Having A Lubricant ReservoirOn The Inner Circumferential Surface,” which discloses PFPE lubricant,is incorporated herein by reference. PFPEs are used as lubricantsbecause they provide excellent lubricity, wide liquid-phase temperaturerange, low vapor pressure, small temperature dependency of viscosity,high thermal stability, and low chemical reactivity. PFPEs also exhibitlow surface tension, resistance to oxidation at high temperature, lowtoxicity, and moderately high solubility for oxygen. Several differentPFPE polymers are available commercially, such as Fomblin Z (randomcopolymer of CF₂CF₂O and CF₂O units) and Y (random copolymer ofCF(CF₃)CF₂O and CF₂O) including Z-DOL and AM 2001 from Montedison,Demnum (a homopolymer of CF₂CF₂CF₂O) from Daikin, and Krytox(homopolymer of CF(CF₃)CF₂O).

Lube layer 121 is typically applied evenly over the disc, as a thinfilm, by dipping the discs in a bath containing mixture of a few percentof PFPE in a solvent and gradually draining the mixture from the bath ata controlled rate. The solvent remaining on the disc evaporates andleaves behind a layer of lubricant less than 100 Angstroms. Recentadvances have enabled the application of PFPE using an in-situ vapordeposition process that includes heating the PFPE with a heater in avacuum lube process chamber. In this system, evaporation occurs invacuum onto freshly deposited DLC protective layer 117 that has not beenexposed to atmosphere, creating a thin uniform coating of PFPE lubelayer 121.

Since it is known in the art that recording media with higher lubricantbonded ratio has better corrosion protection and that an in-situ vaporlubrication process enhances the bonding between lubricants andamorphous carbon, in-situ vapor lubrication has been used to lubricateamorphous carbon layers. In-situ vapor lubrication of recording media isthe lubrication of the recording media immediately after a DLCprotective layer 117 has been deposited over the magnetic layer 113without exposing it to atmosphere. FIG. 1B is a flow chart showing thetypical steps used in an in-situ vapor lubrication process that depositsPFPE lubricant over a carbon layer. The process begins with step 150 bytransferring a partially complete media with substrate 105, seed layer109, and magnetic layer 1113 into a vacuum chamber. In step 155 anamorphous carbon layer is deposited over the partially complete media.Next in step 160, the amorphous carbon is coated with a lube layer 121of PFPE using an in-situ vapor lubrication process. Finally, in step 165the lubed magnetic media is transferred to the next manufacturingoperation.

The same technology, however, works less effectively with a DLCprotective layer 117. When a DLC protective layer 117 is applied overthe magnetic layer 115, unpaired carbon electrons pair with hydrogenelectrons and dangling carbon bonds are tied up, as illustrated in FIG.1C. The termination of the carbon bonds on the surface by hydrogeneffectively reduces the reactive sites. As a result, the bonding sitesfor lubricant molecules are reduced and therefore the lubricant bondedratio decreases. This effect is particularly strong when lubricant isdeposited in-situ after depositing the DLC protective layer 117, asmanifested by the poor adhesion of lube layer 121 to the DLC protectivelayer 117. Because of this effect, IBD or PECVD processes, which produceDLC protective layer 117, and in-situ vapor lubrication processes, whichenhances bonding, have not been combined to achieve the maximumperformance.

Therefore what is needed is a system and method which overcomes theseproblems and makes it possible to use IBD or PECVD processes to depositDLC protective layer 117 and in-situ vapor lubrication processes todeposit lube layer 121 to make a reliable final overcoat.

SUMMARY OF THE INVENTION

In order to improve the adhesion between the diamond like carbon (DLC)protective layer 117, and the lube layer 121, deposited with an in-situlubrication process, the DLC protective layer 117 is depleted ofhydrogen prior to the application of lube layer 121 using in-situ vaporlubrication processes. Depletion of hydrogen activates the surface ofthe DLC protective layer 117 by creating unpaired electrons in the DLCthat are ready to react. The unpaired electrons create a strong bondbetween the DLC protective layer 117 and the lube layer 121.

The DLC protective layer 117 is depleted of hydrogen by bombarding itwith argon ions. The hydrogen atoms are ejected from the surface of theDLC protective layer 117 when the accelerated argon ions collide withthem.

The present invention also can be implemented as a computer-readableprogram storage device which tangibly embodies a program of instructionsexecutable by a computer system to perform a system method. In addition,the invention also can be implemented as a system itself.

These and various other features as well as advantages whichcharacterize the present invention will be apparent upon reading of thefollowing detailed description and review of the associated drawings.

BRIEF DESCRIPTION OF THE INVENTION

FIG. 1A is a block diagram showing a prior art conventional magneticmedia structure;

FIG. 1B is a flowchart illustrating the prior art method of usingin-situ vapor lubrication on a carbon layer;

FIG. 1C is an illustration of a prior art DLC protective layer ready tobe lubed;

FIG. 2 is an illustration of a Hydrogen Depleted DLC (HDDLC) layer,ready for in-situ vapor lubrication, in accordance with an embodiment ofthe invention;

FIG. 3 is a block diagram showing the HDDLC layer 200 in a magneticmedia environment;

FIG. 4 is a flowchart showing the preferred method of depositing theprotective overcoat including the HDDLC layer 200 and the lube layer121;

FIG. 5 is a block diagram showing a thin film deposition system used todeposit the magnetic media structure 300; and

FIG. 6 is an illustration showing details of surface modifier 520 ofsystem 500 of FIG. 5.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention provides a system and method for protecting magneticmedia.

FIG. 2 is an illustration of a Hydrogen Depleted DLC (HDDLC) layer 200,ready for in-situ vapor lubrication, in accordance with one embodimentof the invention. The HDDLC layer 200 includes carbon atoms 210,hydrogen atoms 220, carbon-hydrogen bonds 230, carbon-carbon bonds 240and free dangling carbon bonds 250.

The free dangling carbon bonds 250 are created by bombarding the DLCprotective layer 117 with charged ions as is furthered described withreference to FIG. 4 below. This bombardment process converts the DLCprotective layer 117 into a more reactive HDDLC layer 200 by creatingfree dangling bonds 250. This increases the bonding between the DLCprotective layer 117 and the lubricant that is deposited over it with anin-situ vapor lube process as is described with reference to FIG. 4below.

FIG. 3 is a block diagram showing the HDDLC layer 200 in a magneticmedia environment 300 including a substrate 105, a seed layer 109, amagnetic layer 113 and a lube layer 121. HDDLC layer 200 protectsmagnetic media from wear and tear as does DLC protective layer 117except that it has been modified so that the lube layer 121 adheres toit much better than it otherwise would, providing improved protection.

FIG. 4 is a flow chart showing the preferred steps used to make aprotective overcoat including an HDDLC layer 200 and and in-situ lubedlayer 121. Protective overcoats typically include a hard layer such asDLC and a lubrication layer. The process begins with step 405 bytransferring a partially complete media having substrate 105, seed layer109, and magnetic layer 113 into a vacuum chamber.

Next in step 410, a DLC protective layer 117 containing carbon andhydrogen is deposited onto the substrate. The deposition process can bedone by various thin film deposition techniques including ion beamdeposition (IBD), plasma enhanced chemical vapor deposition (PECVD),magnetron sputtering, radio frequency sputtering or chemical vapordeposition (CVD).

Next in step 415, the DLC protective layer 117 is activated by exposingthe DLC protective layer 117 to argon ions (Ar⁺), from an argon ionplasma, which depletes the DLC protective layer 117 of hydrogen atoms.Exposing includes bombarding the DLC protective layer 117 with ions thatare accelerated by an electric field as well as allowing atoms,molecules or ions to randomly strike the DLC protective layer 117 in theabsence of an electric field. As Ar⁺ ions bombard the DLC protectivelayer 117, hydrogen atoms are ejected, reducing the number of hydrogenatoms left on the DLC protective layer 117, creating an HDDLC layer 200.The depletion of hydrogen activates the DLC by making it a reactivecarbon. The HDDLC is reactive because carbon atoms that were once bondedto hydrogen atoms now have unpaired electrons available for bonding.This preferred process of removing hydrogen atoms from the DLC by Ar⁺ion bombardment is a mechanical process. Step 415 can be done in thesame chamber as that in which the DLC protective layer 117 is depositedor it can be done in a different chamber. If step 415 is performed in asecond vacuum chamber then the partially complete media is transferredto a second chamber after the DLC protective layer 117 is deposited. Thetransferring process is done under vacuum or in an inert environmentsuch as argon.

In the preferred embodiment, the rate at which hydrogen atoms areremoved from the DLC protective layer 117 can be adjusted by changingparameters such as voltages, pressures, flow rates, and temperatures.Voltage controls the electric field acting on the Ar⁺ions andconsequently the force with which Ar⁺ ions bombard the DLC protectivelayer 117. Bombarding occurs when the ions are accelerated towards theDLC protective layer 117, because of the electric field acting on theAr⁺ ions, and collide with the DLC protective layer 117. Pressure andflow rates control physical properties of the plasma such as the numberof Ar⁺ ions available to bombard the DLC protective layer 117.Temperature controls the kinetic energy at the surface of the DLCprotective layer 117 and consequently the amount of energy that must beimparted to the surface to remove hydrogen atoms.

In the preferred embodiment the plasma is made out of ionized argon.Argon is used in the preferred embodiment because it is inert andreadily available. However, other inert gases such as helium (He), neon(Ne), krypton (Kr) or xenon (Xe) can also be used to make up the plasmaof charged ions, which bombard the DLC protective layer 117 and removehydrogen atoms from it. Noble gases are preferred because they are inertand do not chemically react with the DLC protective layer 117. Thisenables the removal hydrogen atoms from the DLC protective layer 117 bythe mechanical process of bombardment. The invention, however, is notlimited to only using noble gases because this process can be carriedout using non-noble gases which do not chemically react with the DLCprotective layer 117. Additionally, this invention is not limited to theremoval of hydrogen atoms from the DLC protective layer 117 bymechanical means only. Other methods such as heating the DLC protectivelayer 117 or chemically reacting another substance with the DLCprotective layer 117 can be used to remove hydrogen atoms from the DLCprotective layer 117.

Next in step 420, an in-situ vapor deposition technique is used to applya lubricant onto a partially completed media completing the protectiveovercoat. In the preferred embodiment PFPE is applied to the partiallycompleted media using an in-situ vapor deposition process that includesheating the lubricant with a heater in a vacuum lube process chamber. Inthis embodiment, evaporation of PFPE occurs in a vacuum onto HDDLC 200after the DLC protective layer 117 has been deposited and its surfacedepleted of hydrogen by exposing it to ionized argon without exposingthe HDDLC 200 to atmosphere.

Finally in step 425 the lubed magnetic media is transferred to the nextmanufacturing operation.

Although the preferred steps used to make a protective overcoat aredescribed in reference to a DLC protective layer 117 and lube layer 121,those skilled in the art will recognize that the same steps can be usedto deposit any two layers, wherein the bonding between the two layers isimproved. For example, a first layer, which can be metallic, insulating,semi-conducting or semi-metallic, can be deposited as described withreference to step 410. The first layer is then activated as describedwith reference to step 415. After the first layer is activated, a secondlayer, which can also be metallic, insulating, semi-conducting orsemi-metallic, can be deposited as described with reference to step 420.The combination of the first layer and second layer can then betransferred to the next manufacturing operation as described in step425.

FIG. 5 represents a multilayer thin film deposition system 500 equippedwith an in-situ DLC deposition system, a carbon surface modifying systemand a vapor lube system. System 500 preferably includes a loader 510, aDLC depositor 515, a surface modifier 520, a vapor luber 525, anunloader 530, a controller 535, a power system 540, a pumping system 545and a gas flow system 550.

Loader 510 and unloader 530 represent conventional load locks that allowsubstrates to be transferred into and out of a vacuum chamber withoutventing the entire vacuum system. DLC depositor 515 represents aconventional thin film deposition chamber used to deposit the DLCprotective layer 117. DLC depositor 515 can use ion beam deposition(IBD), plasma enhanced chemical vapor deposition (PECVD), magnetronsputtering, radio frequency sputtering or chemical vapor deposition(CVD) techniques to deposit the DLC protective layer 117. Surfacemodifier 520 is used to deplete the top surface of the DLC protectivelayer 117 of hydrogen, creating HDDLC layer 200 as is further discussedwith reference to FIG. 4 above. Vapor luber 525 represents aconventional vapor lubing system used to deposit the lube layer 121 ontothe HDDLC layer 200. Controller 535 is the software and hardware whichcontrols the operation of system 500. Power system 540 represents powersupplies used to power the system 500 and include power supplies forheaters, conveyers, DC magnetrons, rf sources. Pumping system 545represents all pumps and valves used to evacuate the vacuum chambersincluding mechanical pumps, turbo pumps, cryogenic pumps and gatevalves. Gas flow system 550 represents the gas delivery equipment suchas mass flow controllers, valves, piping and pressure gauges.

FIG. 6 is an illustration showing surface modifier 520 depletinghydrogen atoms from the top surface of the DLC protective layer 117. Inone embodiment, surface modifier 520 includes a vacuum chamber 605, anargon ion plasma 610, argon ions (Ar⁺) 615, a first voltage V₁ 620, asecond voltage V₂ 625 and a stage 630 depleting hydrogen atoms from thetop surface of the DLC protective layer 117 of a partially completedmedia.

After depositing the DLC protective layer 117, as discussed withreference to FIG. 1B, the top surface of the DLC protective layer 117 isexposed to an argon ion plasma 610 consisting of (Ar⁺) ions 615. In step415, the partially complete media is moved to a grounded vacuum chamber605 which is maintained at process pressures ranging from 10-3 torr to10-2 torr. Power supplies such as the Advanced Energy MDX seriesmanufactured by Advanced Energy of Fort Collins, CO, USA are used tomaintain the DLC protective layer 117 at a first voltage V₁ 615 and theargon ion plasma at a second voltage V₂ 625. The voltage differencebetween the plasma and the DLC protective layer 117 creates an electricfield 630 that accelerates the Ar⁺ ions towards the DLC protective layer117. The actual trajectory 635 of the argon ions depends on many factorsincluding the initial velocity of the ions and the configuration of theelectric field, which is determined by the first voltage 620 and thesecond voltage 625.

It will also be recognized by those skilled in the art that, while theinvention has been described above in terms of preferred embodiments, itis not limited thereto. Various features and aspects of theabove-described invention may be used individually or jointly. Further,although the invention has been described in the context of itsimplementation in a particular environment and for particularapplications, those skilled in the art will recognize that itsusefulness is not limited thereto and that the present invention can beutilized in any number of environments and implementations.

We claim:
 1. A method of preparing a layer comprising, the steps of:depositing a first layer having a first layer surface; activating thefirst layer surface by bombarding the first layer surface with chargedatoms; and depositing a second layer directly onto the first layersurface after said first layer surface has been activated.
 2. The methodof claim 1 wherein depositing is done by ion beam deposition techniques.3. The method of claim 1 wherein the step of activating the first layersurface is depleting the first layer surface of atoms.
 4. The method ofclaim 1 wherein the step of activating the first layer surface isbombarding the first layer surface with charged ions.
 5. A method forpreparing a protective overcoat with in-situ vapor lubrication,comprising the steps: depositing a first layer having carbon andhydrogen onto a medium; depleting said first layer of hydrogen; anddepositing a second layer onto said first layer using an in-situ vapordeposition process, said second layer having a lubricant.
 6. The methodof claim 5 wherein the step of depleting hydrogen includes exposing saidfirst layer to ionized argon gas.
 7. The method of claim 5 wherein thestep of depositing a first layer is done using ion beam deposition. 8.The method of claim 5 wherein the step of depositing a first layer isdone using plasma enhanced chemical vapor deposition.
 9. The method ofclaim 5 wherein the step of depleting hydrogen includes a chemicalprocess for depleting hydrogen.